Wilhelm Roentgen was working on the effects of cathode rays during 1895, when he actually discovered X-rays. His experiments involved the passing of electric current through gases at extremely low pressure. On November 8, 1895 while he was experimenting, he observed that certain rays were emitted during the passing of the current through discharge tube. His experiment that involved working in a totally dark room with a well covered discharge tube resulted in the emission of rays which illuminated a barium platinocyanide covered screen. The screen became fluorescent even though it was placed in the path of the rays, two meters away from discharge tube.

He continued his experiments using photographic plate to capture the image of various objects of random thickness placed in the path of the rays. He generated the very first “roentgenogram” by developing the image of his wife Anna’s hand and analyzed the variable transparency as showed by her bones, flesh and her wedding ring. Terrified, Anna famously cried out, “I have seen my death!”

Based on his subsequent research and experiments, he declared that X-ray beams are produced by the impact of cathode rays on material objects. He named the new ray X-ray, because in mathematics “X” is used to indicated the unknown quantity. His discovery revolutionized the entire medical profession and set foundation for diagnostic radiology. In 1901, Roentgen received the first ever Nobel Prize in Physics.

It would be nearly a decade before scientists discovered X-rays had harmful effects. Clarence Dally, one of Thomas Edison’s assistants, died of skin cancer in 1904 after working with the radiation. Without a full grip on the consequences, standards for protection did not come into force until the 1950s — by that time some stores in America had been helping people to see how well shoes fit by looking through an X-ray machine for decades!

Reference:

http://www.mapsofworld.com/on-this-day/november-8-1895-ce-wilhelm-rontgen-accidentally-discovers-the-x-ray

https://explorable.com/wilhelm-conrad-roentgen

https://www.nde-ed.org/EducationResources/HighSchool/Radiography/discoveryxrays.htm